Geomaterials, 2011, 1, 21-23
doi:10.4236/gm.2011.11003 Published Online April 2011 (http://www.SciRP.org/journal/gm)
Methane Formation by the Reaction of Coalbed
Carbon with Water
V. E. Vigdergauz
Russian Academy of Sciences, Moscow, Russia
Received February 14, 2011; revised March 2, 2011; accepted March 21, 2011
Abstract
There is proposed a mechanism of methane and carbon dioxide formation by the direct reaction of carbon with water
during catastrophic events in the mining of coal deposits. Thermodynamics of the reaction is discussed.
Keywords: Methane Formation, Coal Mining, Water, Carbon Dioxide, Reaction Thermodynamics
1. Introduction
Mechanism of methane formation is a key question in an
understanding of the reasons of its “huge reserves” and
the role in “unpredictable catastrophes” [1]. There are
three main reasons for our interest to the problem [2]:
Association of methane with coal has always pre-
sented a safety problem in mines due to the potential for
explosions. Mixtures of methane and air, with the meth-
ane content between 5 and 14 percent by volume, are
explosive. Explosions of such mixtures have been fre-
quent in coal mines and collieries and have been the
cause of many mine disasters;
Interest in the recovery of methane from coalbeds has
increased rapidly over recent years, because of its poten-
tial as an energy resource and to alleviate pollution and
safety problems;
Methane contributes to the adverse environmental im-
pacts of global warming, tropospheric ozone formation
(smog), and potentially stratospheric ozone destruction.
Its evolution during exploitation of coal deposits is a
source of numerous speculations but not really under-
standable till now. Traditionally three mechanisms for
methane formation are considered [2]: (1) nonbiogenic
formation, (2) formation by anaerobic bacteria during
plant material deposition and the early stages of diagene-
sis, and (3) formation from pyrolysis of coal material
during coal maturation.
All three mechanisms do not explain a fast and unpre-
dictable evolution of huge amounts of the gas in the
processes of an exploration of coal deposits. Controver-
sies are connected with the attempts to consider desorp-
tion of methane from the coal despite of its formation.
It is well known that in the case of catastrophic events
during exploitation of coal deposits there are observed
sudden waste of methane and carbon dioxide. One of the
biggest sudden wastes of gases from the coal occurred in
1921 in France in the Gard district on the mine Nord'Alle
[1]. Of the deposit sudden burst such amount of carbon
dioxide that it flood the mine, poured on the surface and
submerge small town that was situated in the lowlands.
During the catastrophic events the volume of the emit-
ted gases in some cases could reach hundreds cubic me-
ters per tone of the thrown coal. The process that leads to
such catastrophic events is not quite understandable till
now. We know two products of the reaction - methane
and carbon dioxide, and one of the reactants – coalbed
carbon. Coal substance contents some amounts of hydro-
gen but these quantities are too small for the balance. The
main question is the source of the huge amounts of hy-
drogen and a probable answer that it is water.
From the practice of coal mining it is known the cool-
ing of the coal bed before the sudden waste [1] that is
shows the endothermic character of the processes which
are observed before the sudden waste event.
The goal of the presented paper is to check up a ther-
modynamic probability of methane nonbiogenic forma-
tion directly from coalbed carbon and water in the condi-
tions of exploitation of coal deposits.
2. Reaction Termodynamics
According to Gibbs equation Gibbs free energy change
under standard conditions is equal to the total energy
changes for the system minus energy lost in the disor-
dering of the system:

22 Methane Formation by the Reaction of Coalbed Carbon with Water
SGHT (1)
There are two common methods of calculating of Δ G
for chemical reactions - determine Δ Hrxn and Δ Srxn and
use Gibbs equation or use tabulated values of free ener-
gies of formation, ΔGf.
The table summarizes molar thermodynamic charac-
teristics of substances which will be used for an analysis.
Standard molar thermodynamic characteristics of sub-
stances [3].
Substances Δ Hf298,kJ/mol Δ
S298,J/mol.K
Δ
Gf298,kJ/mol
C (s), graphite 0 32.1 -9.566
H2O(l) -285.83 69.95 -306.675
O2(g) 0 161.1 -48.008
CH4(g) -74.87 188 -130.894
CO(g) -110.53 197.66 -169.433
CO2(g) -393.52 213.79 -457.229
Proposed model describes a formation of methane
from a coal by the direct interaction of carbon with water.
Direct reduction of hydrogen from its oxide by coal in
the form of graphite carbon could be represented by the
equation:
2C + 2H2O = CH4 + CO2 (2)
rxn
G

= 44.36 kJ/mol of methane
The above reaction 2 is an endothermic one, but the
products entropy increases and the reaction could be
product-favored. Changes of the reaction 2 entropy Δ Srxn
= 197.69 J/mol.K is positive and this reaction could be an
“entropy driven”.
Necessary energy could be produced by parallel exo-
thermic processes of partial or total oxidation of methane,
such as:
CH4 + 2O2 = CO2 + 2H2O (3)
ΔGrxn = - 843.67 kJ/mol of methane
Summary processes of the generation of coalbed meth-
ane and its explosive oxidation are highly exothermic.
Scheme illustrates energy change during the process of
formation and subsequent oxidation of coal methane:
Energy change during the process of formation and subsequent oxidation of coal methane.
Summary energetic effect of carbon oxidation through
the pass with methane formation is near 400 kJ/mol of
carbon.
Reaction energy is undependable from its path and di-
rect oxidation of carbon by oxygen on the reaction:
C + O2 = CO2 (3)
ΔG rxn = - 400 kJ/mol
gives the same energy and the differences are only in the
reaction path and in the values of activation energies.
3. Field Observations
The proposed path of methane formation on the reaction
of water with coal carbon is indirectly confirmed by the
results of environment chemical analysis. By an exten-
sive study of the hydrologic situation in the Fruitland
Formation it was shown that the continuity of water cov-
erage of the formation is a crucial question for the for-
mation of methane from coal beds [4]. Chemical analysis
of gas and water phases in the areas of Coal-bed Meth-
ΔG
0
CH4 + CO2
2C + 2H2O
2O2
2CO2 + 2H2O
Reaction path

Methane Formation by the Reaction of Coalbed Carbon with Water 23
ane (CBM) formation also confirms the proposed
mechanism [5]. It was observed, that generally, dissolved
anions in water co-produced with CBM contain mainly
bicarbonate (HCO3
−) and chloride (Cl−). The bicarbonate
quantity decreased because this component limits the
amount of calcium (Ca) and magnesium (Mg) through
the precipitation of carbonate minerals. The composition
is controlled in great part by the association of the waters
with a gas phase containing varying amounts of carbon
dioxide (CO2) and methane. Indirect evidence about re-
ductive conditions during CBM formation gives an ob-
servation that “CBM waters are relatively low in sulfate
(SO4) because the chemical conditions in coal beds favor
the conversion of SO4 to sulfide”.
Shvartsev et al. [6] have recently shown for the
Erunakovo region of the Kuznetsk origin (Russia) that
during the coal methane formation a high mineralization
of water and the higher contents of HCO3
− is mainly
observed due to CO2 formation, which is not the product
of mantle genesis but is the product of coal metamor-
phism.
It is mentioned that coal rank increases with burial
depth and CBM content increases with increasing rank,
so that with greater seam depths, gas contents are ex-
pected to increase [7].
In conditions of high pressure and heating (for events
of methane blast, for example) the reduction of hydrogen
from its oxide could possess as chain-type reactions on
the free radical-mechanism:
C + H2O = CH˙ + OH˙… CH˙ + H2O = CH2˙ + OH˙…
CH2˙ + H2O = CH3˙ + OH˙… CH3˙ + H2O = CH4 + OH˙…
(4)
C + 3OH˙ = CO2 + H3O˙… OH˙ + H2O = H3O˙…
C + H3O˙ = H2O + CH˙; C + H˙ = CH˙… et cetera.
The rate of release of methane depends on the tem-
perature and pressure in the coalbed, coal rank and the
size of coal particles.
By the study of temperature–pressure conditions in
coalbed methane reservoirs of the Black Warrior basin
Pashin and McIntyre [8] have recently shown that carbon
sequestration and enhanced coalbed methane recovery
show great promise in subcritical reservoirs.
Presence of water seems necessary for methane for-
mation and methane sudden waste due to desorption
processes only does not explain the phenomena quantita-
tively. Mechanism of methane formation by a slightly
endothermic reaction of carbon and water simultaneously
with highly exothermic processes of the oxidation in the
coal bed explains unpredictable evolution of the huge
amounts of methane during exploitation of coal deposits.
4. Conclusions
Reaction of methane formation from carbon and water is
a slightly endothermic process. Its energy could be com-
pensated by exothermic reactions of partial or total oxi-
dation of methane in the conditions of exploitation of
coal deposits. The proposed mechanism of methane for-
mation is confirmed by the results of the analysis of the
hydrologic situation in the areas of coal-bed methane
formation.
5. References
[1] I. L. Ettinger, “Huge reserves and unpredictable catas-
trophes,” Moscow: Science, 1988.
[2] V. J. Hucka and D. M. Bodily, “Methane Formation in
Utah Coals,” SME 1993, Internet Available:
http://www.onemine.org/search/summary.cfm/Methane-
Formation-In-Utah-Coals?d=838F8CCB0E722E7EFD18
B682C551854549145D57558153FB4E7FFCF7CA897C
2F5766.
[3] http://en.wikipedia.org/wiki/Methane_(data_page)#Ther
modynamic_properties
[4] U. Fehn, G. Snyder, W. C. Riese, et al., Coal bed meth-
ane formation and water movement: application of the
I-129 and Cl-36 systems,” 2001, Paper 23-0 GSA Annual
Meeting.
[5] U. S. Department of the Interior, U. S. Geological Survey,
USGS Fact Sheet FS-156-00, November 2000
http://pubs.usgs.gov/fs/fs-0156-00/
[6] S. L. Shvartsev, V. T. Khryukin, E. V. Domrocheva, et al,
“Hydrogeology of the Erunakovo region of the Kuznetsk
basin in the context of coal methane formation and min-
ing,” Russian Geology and Geophysics. Vol. 47, no.7,
2006, pp. 878-889.
[7] http://www.ags.gov.ab.ca/energy/cbm/coal_and_cbm_intr
o2.html
[8] J. C. Pashin and M. R. McIntyre, “Temperature–pressure
conditions in coalbed methane reservoirs of the Black
Warrior basin: implications for carbon sequestration and
enhanced coalbed methane recovery,” Int. J. Coal Geol.
Vol. 54, 2003, pp. 167-183.